Electronic stimulation systems may be used to control pain or motor disorders. Such systems have also been used to stimulate bone growth. For example, application of an electrical field to spinal nervous tissue can effectively mask certain types of pain transmitted from regions of the body associated with the stimulated tissue. More specifically, applying particularized electrical pulses to the spinal cord associated with regions of the body afflicted with chronic pain can induce paresthesia, or a subjective sensation of numbness or tingling, in the afflicted bodily regions. This paresthesia can effectively inhibit the transmission of non-acute pain sensations to the brain.
Electrical energy, similar to that used to inhibit pain perception, may also be used to manage the symptoms of various motor disorders, for example, tremor, dystonia, spacticity, and the like. Motor spinal nervous tissue, or nervous tissue from ventral nerve roots, transmits muscle/motor control signals. Sensory spinal nervous tissue, or nervous tissue from dorsal nerve roots, transmit pain signals.
Electrical energy may be commonly delivered through electrodes positioned external to the dural layer surrounding a spinal cord. The electrodes are carried by two primary vehicles: the percutaneous lead and the laminotomy lead.
Percutaneous leads commonly have two or more electrodes and are positioned within an epidural space through the use of an insertion, or Touhy-like, needle. An example of an eight-electrode percutaneous lead is an OCTRODE® lead manufactured by Advanced Neuromodulation Systems, Inc.
Operationally, an insertion needle is passed through the skin, between the desired vertebrae, and into an epidural space which is defined by a dural layer in combination with the surrounding vertebrae. The stimulation lead is then fed through the bore of the insertion needle and into the epidural space. Conventionally, the needle is inserted at an inferior vertebral position, for example, between vertebrae L1 and L2 (L1/L2), and the stimulation lead is advanced in a superior direction until the electrodes of the stimulation lead are positioned at a desired location within the epidural space, for example, at T10. In a lateral position, percutaneous leads are typically positioned about a physiological midline.
As an example of application, the above methodology is commonly used for the management of sympathetically maintained pain (SMP). It is generally believed that due to the sympathetic nature of SMP, stimulation leads positioned about a physiological midline provide sufficient electrical energy to interrupt the transmission of SMP signals. However, the above-described conventional technique may be used for the management of sympathetically independent pain (SIP), stimulating bone growth, and treating muscle disorders, among others.
Spinal Cord Stimulation (SCS) systems are of two types. The most common system is a totally implanted pulse generator (IPG). An IPG consists of a surgically implanted, internally-powered pulse generator and, typically, a single multi-electrode lead. The internalized power source limits the life of these systems to between one and four years. After the power source is expended, the patient is required to undergo replacement surgery to continue electrical stimulation.
The second type of SCS system is a radio frequency (RF) system. An RF system consists of a surgically implanted, passive receiver and a transmitter which is worn externally. The transmitter is connected to an antenna which is positioned externally, over the site of the implanted receiver. In operation, the transmitter communicates through an RF signal, to the implanted receiver. Just as with the IPG system, electrical stimulation is delivered via implanted leads. Differing from an IPG, however, RF systems typically possess greater power resources, thereby enabling RF systems to utilize multiple leads.
As an alternative to spinal cord stimulation, electrical energy may be delivered to selected peripheral nerves using a peripheral nerve stimulation system. Peripheral nerve stimulation involves administration of electrical energy to a localized group of peripheral nerves through placement of one or more leads at the peripheral nerve site. Unfortunately, if a patient's pain is widespread, a patient may require a plurality of stimulation leads to be implanted. The surgical procedure necessary for stimulation lead implantation is significant and can be quite painful. Additionally, because peripheral stimulation leads are implanted in “active” areas of the body (e.g., arms and legs), the leads typically lack long-term placement stability. Lead movement, or lead migration, can affect the quality of pain relief. Further, significant lead movement that undermines the intended stimulation effect may require additional corrective surgeries to reposition the stimulation leads.
In each of these cases, the stimulation device may be coupled to one or more leads with one or more electrodes. Depending on the application and the purpose of the stimulation, varying stimulation patterns and electrical fields may be desired. An applied electrical field is defined by the polarity of each electrode of the stimulation lead. Conventionally, each electrode is set as an anode (+), cathode (−), or neutral (off). For a four electrode percutaneous lead there exists approximately 50 electrode combinations. For an eight electrode percutaneous lead, the number of possible electrode combinations grows to approximately 6050. Further, various combinations of pulses and pulse frequencies may be using with sets of electrodes.
Since many typical stimulation devices are implanted in a patient, these stimulation devices have a limited power source or require periodic charging with an RF charger. In a unit having a limited power source, costly surgery is performed to service the unit and replace the power source. In RF charged units, patients must remember to periodically charge the unit.
In a typical stimulation device, patients are encouraged to turn the units off as often as possible. Alternately, the units are cycled on and off so that the tissue is stimulated for a period of time, then not. When the stimulation is used to mask pain, turning the unit off or cycling the unit on and off may cause considerable discomfort. Further, the patient may simply ignore the request to turn the unit off.
As such, many typical stimulation devices suffer from limited power sources or periodic recharging requirements. Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.